1. Field of the Invention
This invention relates to a metal oxide solid solution comprising an oxide of a Group II metal of the periodic table, titanium oxide and silicon oxide as main components, and more specifically, to a novel crystalline metal oxide having main peaks at about 26.7.degree. and about 20.9.degree. in its Cu-K.alpha. X-ray diffraction pattern (2.theta.) and a specific refractive index, and a process for the production thereof.
2. Description of the Prior Art
Alpha-quartz, known as one crystalline metal oxide, has been used in various applications. Artificial preparation of this quartz requires a process involving growth of crystal particles at high temperatures and pressures, and therefore, the process is too expensive to gain full industrial acceptance. It has been desired therefore to develop a technique of producing alpha-quartz under mild manufacturing conditions. To date, however, no industrial process for producing alpha-quartz under mild conditions has been established.
Although not with a view to producing alpha-quartz, Yamane et al. produced a gel composed of SrO--SiO.sub.2, and found that when this transparent gel was heated at about 600.degree. C., it became whitely turbid. They presumed this phenomenon to be due to the formation of alpha-quartz. [Journal of Non-Crystalline Solids, 44 (1981), 181-190: "Low Temperature Synthesis of Non-Crystalline Solids of the System SrO--SiO.sub.2 "]. The phenomenon found by Yamane et al. is interesting, but repetition of this experiment by the present inventors has shown that the white turbidity was due to the formation of cristobalite, and alpha-quartz could not be produced.
In the field of improving the hardness of synthetic resins or reinforcing them, it has recently been desired to develop inorganic compounds having superior properties which meet this purpose, particularly spherical (pearl-like), film-like or fibrous inorganic oxides. It would be especially significant to establish a technique of producing alpha-quartz having various shapes such as spheres, fibers, films, etc. industrially under mild conditions.